Earth Tripping

[twm.bwen]

Hi there,
I was replacing a broken 2g socket when the trip switch went even though the circuit MCB and the CU RCD were both turned off. I found out it was because the negative wire earthed itself on the knock out box. I've tried to find out why on tinternet but can find no answers. Wny is it happening, is it potenrially dangerous and how can it be rectified?

Thanks

Tom

 

[Steve]

neutral earth fault you're creating. Perfectly normal. When you turn off the circuit you only isolate the live. Because the neutral and earth are therefore still connected, a small amount of current can flow when they touch, and trip the RCD.

 

[RF Lighting]

You say the trip switch went, but you had turned off the MCB and the RCD.

What is this trip switch you speak of?

What is written on it?

 

[twm.bwen]

Sorry, when I meant trip switch I meant the 80Amp RCD that is between the meter and the CU. RCD on CU off, and individual MCB off, negative touches earth and the aformentioned 80amp RCD trips despite neither CU or circuit being live.
Thanks

 

[JohnD]

You have an RCD in the CU and another in the tails? Are you sure the one in the CU is an RCD and not a DP switch?

What is written on each of them?
clue: One might say 30mA and one might say 100mA "S" type.

Or perhaps you have a not very elegantly designed installation.

 

[securespark]

Or have you got RCBO's?

 

[RF Lighting]

Or better still you could post a photo of your mains and intake.

 

[securespark]

I'm gonna back off, now...

 

[JohnD]

Secure's suggestion could have been a very elegant design.

 

[securespark]

With the emphasis on could....

 

[JohnD]

... if it had been designed by someone who understood the glorious advantages of those splendid devices

 

[twm.bwen]

Ok so I think I have confused the DP Isolator Switch with a trip switch.
My set up is thus, 2 Mains comes into the house into 2 100A fuses then onto the meter. The tails then come fromthe meter to the 80Amp Residual Current Ciruit Destroyer (trip switch) with its test button, then onto the CU with a double pole Isolator switch and individual MCBs.

So back to my intitial problem, is this normal for the RCCD to trip when the negative earths itself despite the DPIS and MCB being off?
, if not what can I do about it?

 

[JohnD]

If the DP isolator was off, I would not have expected the RCD to trip, because there should have been no current flowing. However there can be odd small currents flowing, especially if you live in a semi or similar house, when small currents from next door sometimes come up through the water pipes.

Can you lay your hands on a digital camera and put up a pic of the area showing the meter, tails, fuses, RCD and CU? It might be helpful if we could see how it is set up.

Ta.

 

[slippyr4]

2 Mains comes into the house into 2 100A fuses then onto the meter.

2 fuses? Are they both on the live? or is there one on live and one on neutral?

A fuse in the neutral is dangerous. Perhaps you're confusing a thing on the neutral with a fuse when it's not actually a fuse.

 

[Steve]

PICTURES!!!!